I installed some of this
3M Sound Deadening Pad on the wheel wells. It's self adhesive and it works well. I lifted the car, removed the rear wheels, cleaned the wheel wells with soap and water, let it dry and went at it. Where I could install full sheets I did and were I couldn't I cut pieces to fit almost like a jigsaw puzzle. It completely eliminated the dinging rock/stone sounds inside the cabin and made it overall quieter. I drove around yesterday in the heat of the day and the hot highway and the hot exhaust/brakes didn't affect it, the pads stayed on. I used 6 sheets and had about half of one left, the material is very malleable and heavy too; the 6 sheets weighed in at 30 lbs. I haven't driven in the rain so I don't know how it'll do once it gets wet but the adhesive is very good. I think it took about 3 hours to do both rear wheel wells. Lots of work! I did this to eliminate the rock/stone dinging sounds back there, you still have the regular road noise which comes in through the spare tire and hatch area behind the seats but no more rock noises.